Electromechanical transducer controlling device

ABSTRACT

A device for controlling an electromechanical transducer such as a proportional electromagnetic valve, in which a pulse signal having a constant period shorter sufficiently than the minimum response time required for the displacement of the plunger of the proportional electromagnetic valve over its predetermined full stroke is applied to the electromagnetic coil of the proportional electromagnetic valve to superpose a very small vibratory stroke component on the stroke of the plunger, and the duty cycle of the pulse signal applied to the electromagnetic coil is varied so as to urge the plunger in directly proportional relation to the variation of the duty cycle without substantially giving rise to mechanical hysteresis in the stroke of the plunger.

This is a continuation of application Ser. No. 891,003, filed Mar. 28,1978, now abandoned.

LIST OF PRIOR ART REFERENCES (37 CFR 1.56 (a))

The following reference is cited to show the state of the art:

U.S. Pat. No. 3,981,288--Wolf Wessel--Sept. 21, 1976--123-139

BACKGROUND OF THE INVENTION

This invention relates to a device for controlling an electromechanicaltransducer delivering a mechanical quantity as its output correspondingto the magnitude of an electrical quantity applied as its input, andmore particularly to a control circuit for accurately driving aproportional electromagnetic valve as instructed by an electricalinstruction signal.

As the regulations on the toxic components in the exhaust gas ofinternal combustion engines of motor vehicles have been made morerigorous in recent years, there has arisen a demand for an exhaust gaspurification system which can quickly and accurately remove the toxiccomponents in the exhaust gas without appreciable aging and with highreliability. In an effort to comply with this demand, various exhaustgas purification systems have been proposed, and as a consequence ofextensive researches and studies by the parties concerned, the exhaustgas purification systems have been steadily developed to the practicallyusable stage. Among the proposed and developed systems, the controlsystems including means for ensuring the reliability and reproducibilityof control and capable of compensating the aging and other problems areconsidered most promising. A closed-loop control system controlling theair-fuel ratio in the carburetor utilizing a ternary catalyst, and anengine combustion control system utilizing a microcomputer for theair-fuel ratio control are examples of the promising control systems. Insuch a control system, an electromechanical transducer is essentiallyrequired which can quickly and accurately respond to an instructionsignal applied from a control circuit. A variety of suchelectromechanical transducers are presently under investigation by theparties concerned and include:

(1) An electromechanical transducer (a proportional electromagneticvalve) delivering a mechanical quantity as its input corresponding tothe magnitude of an electrical quantity applied as its input;

(2) an electromechanical transducer (an on-off electromagnetic valve)delivering a mechanical quantity as its output which takes either aminimum value or a maximum value depending on whether an electricalquantity applied as its input has a level higher or lower than apredetermined threshold level; and

(3) an electromechanical transducer in the form of a servomotor or astepping motor.

The electromechanical transducer in (3) includes the problems of highcost, low control accuracy, slow response, etc. compared with those in(1) and (2), and investigations on the electromechanical transducers in(1) and (2) are presently extensively being done.

However, the electromechanical transducers in (1) and (2) include alsotheir own peculiar problems. The electromechanical transducer in (1), orthe proportional electromagnetic valve, includes the following problems:

(a) The proportional electromagnetic valve is the electromechanicaltransducer which delivers a mechanical quantity, that is, displacementor force as its output corresponding to the magnitude of an electricalquantity, that is, current supplied as its input. It is thereforenecessary to subject an output signal of its control circuit todigital-analog (D-A) conversion when a digital means such as amicrocomputer is used therewith.

(b) Hysteresis tends to occur in the mechanical quantity, and theaccuracy of control tends to be reduced. The term "hysteresis in themechanical quantity" is used herein to denote such a phenomenon that theposition of the plunger of the electromagnetic valve responding to aconstant current value supplied to the electromagnetic coil differsdepending on whether the plunger makes an advancing stroke or aretracting stroke. It will thus be obvious that this hysteresis impairsthe performance of the proportional electromagnetic valve.

(c) Means for counterbalancing the electromagnetic force, that is, aspring system is used to provide the mechanical quantity correspondingto the electrical quantity. Consequently, the proportionalelectromagnetic valve tends to be adversely affected by disturbance suchas vibration externally impacted thereto.

On the other hand, the electromechanical transducer in (2), or theon-off electromagnetic valve, includes the following problems:

(d) The on-off electromagnetic valve is the electromechanical transducerwhich delivers a mechanical quantity, that is, displacement as itsoutput which takes a minimum value or a maximum value depending onwhether an electrical quantity applied as its input has a level higheror lower than a predetermined threshold level. That is, the on-offelectromagnetic valve has such a property that it does not produce anymechanical displacement unless a predetermined electrical quantity isapplied as its input. In order to derive the mechanical quantitycorresponding to the electrical quantity, therefore, it is necessary tocontrol the duty cycle of the electrical quantity applied to the on-offelectromagnetic valve for directly controlling a pressure, for example,the differential pressure across the air jet, or to utilize a pressuremedium, for example, the engine suction vacuum or Venturi vacuum as anactuating source and control the magnitude of this actuating source forindirectly controlling a pressure responsive means such as a diaphragmmeans which converts a pressure into a mechanical quantity such asdisplacement. Therefore, even when the electrical quantity applied tothe on-off electromagnetic valve as its input exceeds the predeterminedthreshold level within a short period shorter than the minimum responsetime required for the mechanical quantity (displacement) to reach itsmaximum value from its minimum value, the on-off electromagnetic valvecannot mechanically follow the variation of the input within such ashort period, and no variation occurs in the mechanical quantity. Thus,the mechanical quantity does not vary in the region in which the on-offperiod ratio, that is, the duty cycle of the electrical quantity inputis small, and a dead zone of control results. This dead zone will beexplained with reference to FIG. 1. Suppose that TB and TA represent theon-state period of a voltage V applied to the on-off electromagneticvalve, and one cycle of the applied voltage V respectively. Then, thestroke of the plunger of the electromagnetic valve is zero, that is, theplunger makes no displacement when the on-state period TB is short, orwhen the duty cycle is small. The dead zone appears in such a case.

(e) Due to the continual reciprocating movement of the means fortransmitting the mechanical quantity, for example, the needle valvemember between the minimum value and the maximum value of its fullstroke, considerable material wear occurs at the parts such as thebearing, valve seat and stopper engaged and struck by the needle valvemember, and a considerable crashing sound is also produced at the partsstruck by the needle valve member.

(f) Since the duty cycle of the electrical quantity applied to theon-off electromagnetic valve is controlled to control the mechanicaloutput of the valve between its minimum value and its maximum value,vibration or pressure ripple tends to occur in the final mechanicalquantity, for example, the air jet negative pressure.

As pointed out above, both the proportional electromagnetic valve in (1)and the on-off electromagnetic valve in (2) have included their ownpeculiar problems, and it has been demanded to make further improvementsto obviate these problems of the electromechanical transducers so thatthe transducers can be reliably used in motor vehicles for variouscontrol purposes.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to obviate the prior artproblems pointed out above and to provide a novel and improved controldevice for an electromechanical transducer of the kind which provides amechanical output proportional to an electrical input quantity so thatsuch a transducer can respond accurately to the input.

The present invention is applied specifically to the control of theelectromechanical transducer or the proportional electromagnetic valvedescribed in (1) and is featured by the provision of control means whichcontrols an electrical input signal to the electromechanical transduceras follows:

(a) The transducer is controlled by a cyclic electrical input signal soas to alleviate the material wear due to the striking of the slidingparts against the associated parts and to reduce the level of thecrashing sound.

(b) On-off of the electrical quantity applied as the input to thetransducer is repeated at a constant period shorter than the minimumresponse time required for the full stroke of the plunger urged by themechanical output of the transducer, and the duty cycle of theelectrical input is controlled so as to provide an analog mechanicaloutput or quantity, for example, displacement which can be controlled bya digital electrical signal.

(c) By virtue of the manner of control described in (b), the analogmechanical quantity includes a very small digital quantity component ora very small vibratory stroke component which is effective ineliminating the hysteresis occurring in the mechanical output of thetransducer.

(d) Two switching elements are provided for the cyclic on-off of theelectrical quantity applied to the transducer, and electrical signalshaving opposite duty cycles such that one of them is in its on-statewhile the other is in its off-state are applied to these two switchingelements respectively. Therefore, current supplied to the member or thecoil generating an electromagnetic force corresponding to the magnitudeof the electrical quantity input can flow in either the positivedirection or the negative direction depending on the ratio between theduty cycles of the electrical inputs applied to the respective switchingelements so as to provide the analog mechanical quantity, for example,the displacement of both the positive direction and the negativedirection.

(e) Application of the control means in (b) as an actuating means forthe closed-loop air-fuel ratio in a carburetor utilizing a ternarycatalyst can minimize the hysteresis in the mechanical quantity therebyimproving the accuracy of control of the air-fuel ratio. In addition,elimination of the necessity for digital-analog (D-A) conversion canreduce the cost of the electrical circuit and improve the reliability ofthe electrical circuit.

(f) Application of the control means in (b) as an actuating means forthe control of the recycled exhaust gas quantity in an engine combustioncontrol system provided with a microcomputer can minimize the hysteresisin the mechanical quantity thereby improving the accuracy of control ofthe recycled quantity of exhaust gas. In addition, elimination of thenecessity for D-A conversion can reduce the cost of the electricalcircuit and improve the reliability of the electrical circuit.

(g) Application of the control means in (b) as a means for controllingthe air-fuel ratio in an engine combustion control system provided witha microcomputer can attain the effect similar to that described in (e).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the operating characteristic of an on-offelectromagnetic valve to illustrate the presence of a dead zone.

FIG. 2 is a partly sectional side elevational view showing the structureof a so-called plunger type proportional electromagnetic valve.

FIG. 3 is a partly sectional side elevational view showing the structureof a so-called moving-coil type proportional electromagnetic valve.

FIG. 4A shows the waveform of a voltage applied generally as an input tosuch an electromagnetic valve.

FIG. 4B shows the stroke response characteristic of the plunger of suchan electromagnetic valve responding to the input voltage shown in FIG.4A.

FIG. 4C shows the waveform of a control signal voltage having a periodT₃ shorter than the time T₁ required for the full stroke of the plungerof the electromagnetic valve, such a voltage waveform being employed forthe control by the control device according to the present invention.

FIG. 4D shows the stroke characteristic of the plunger of theelectromagnetic valve responding to the voltage input signal shown inFIG. 4C.

FIG. 5 is a circuit diagram of an embodiment of the control deviceaccording to the present invention.

FIG. 6A is a control signal waveform diagram similar to FIG. 4C employedfor the control of the electromagnetic valve by the control deviceaccording to the present invention, but showing three different on-stateperiods T₄, T₅ and T₆ for the same period T₃.

FIG. 6B is a waveform diagram of current supplied to the coil of theelectromagnetic valve to show three different current waveformscorresponding respectively to the three signal waveforms shown in FIG.6A.

FIG. 6C is a waveform diagram of the stroke of the plunger of theelectromagnetic valve to show three different stroke waveformscorresponding respectively to the voltage and current waveforms shown inFIGS. 6A and 6B.

FIG. 7A is a graph showing the relation between the duty cycle and thecoil current of the electromagnetic valve controlled by the controldevice according to the present invention.

FIG. 7B is a graph showing the relation between the coil current and thestroke of the plunger of the electromagnetic valve controlled by thecontrol device according to the present invention.

FIG. 7C is a graph showing the relation between the duty cycle and thestroke of the plunger of the electromagnetic valve controlled by thecontrol device according to the present invention.

FIG. 8 is a circuit diagram of another embodiment of the presentinvention for controlling an electromechanical transducer or aproportional electromagnetic valve.

FIG. 9 is a graph showing the relation between the duty cycle and thestroke of the plunger of the proportional electromagnetic valvecontrolled by the control device shown in FIG. 8.

FIGS. 10 to 15 show applications of the control device according to thepresent invention to various control systems, wherein:

FIG. 10 is a system diagram of a control system in which the controldevice according to the present invention is used as an actuating meansfor the closed-loop air-fuel ratio control in a carburetor utilizing aternary catalyst;

FIG. 11 is a partly sectional side elevational view of part of a controlsystem in which a single electromagnetic valve controlled by the controldevice according to the present invention is used to control a pluralityof metering jets;

FIG. 12 is a system diagram of an engine combustion control systemprovided with a microcomputer, in which the control device according tothe present invention is used as an actuating means for the control ofthe recycled exhaust gas quantity;

FIG. 13 is a system diagram of part of a control system in which anelectromagnetic valve controlled by the control device according to thepresent invention is used to control a pressure thereby controlling theflow rate of fluid;

FIG. 14 is a system diagram of part of a control system in which theelectromagnetic force generated by an electromagnetic valve controlledby the control device according to the present invention is used tocounterbalance the force of a return spring in a pressure regulatingvalve; and

FIG. 15 is a system diagram of a mechanical fuel injection system inwhich an electromagnetic valve controlled by the control deviceaccording to the present invention is used to control the quantity offuel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 2 and 3 show schematically the structure of two types of theaforementioned proportional electromagnetic valve, that is, FIG. 2 showsthe structure of a so-called plunger type proportional electromagneticvalve, and FIG. 3 shows the structure of a so-called moving-coil typeproportional electromagnetic valve.

Referring to FIG. 2, the so-called plunger type proportionalelectromagnetic valve is shown comprising a coil 101 for generating anelectromagnetic force, a plunger 102 making displacement proportional tothe electromagnetic force generated by the coil 101, a needle valvemember 103 following the displacement of the plunger 102 for controllingthe open area of an associated controlled element, a bearing 104 forensuring smooth reciprocating movement of the needle valve member 103, acoil spring 105 for stably holding the plunger 102 in its initialposition and counter balancing the electromagnetic force generated bythe coil 101 to determine the displaced position of the plunger 102, andan external terminal 106 for supplying current to the coil 101.

Referring to FIG. 3, the so-called moving-coil type proportionalelectromagnetic valve is shown comprising a magnet 107 for generating amagnetic field, an outer yoke 109 and an inner yoke 110 for directingpart of the magnetic field generated by the magnet 107 toward a coil108, a coil bobbin 111 for fixedly carrying the turns of the coil 108wound therearound, an external terminal 112 for supplying current to thecoil 108, a coil spring 113 for counterbalancing the force generated bythe coil 108 to permit proportional displacement of the coil 108 andcoil bobbin 111 (both of which will be generally referred to as a movingcoil hereinafter), a needle valve member 114 following the displacementof the moving coil for controlling the open area of an associatedcontrolled element, and a bearing 115 for ensuring smooth reciprocatingmovement of the needle valve member 114.

Such electromagnetic valves have a response characteristic as shown inFIGS. 4A and 4B. When a step voltage as shown in FIG. 4A is applied tothe coil of such an electromagnetic valve, the electromagnetic valveresponds to the applied voltage with a stroke characteristic as shown inFIG. 4B. It will be seen from FIG. 4B that a time lag of first order T₁occurs in the stroke of the plunger or needle valve member due to thedelayed response during the rise time of current supplied to the coil101 or 108 of the electromagnetic valve and also due to, for example,the resistance of the bearing 104 or 115 against the sliding movement ofthe needle valve member 103 or 114. When the step voltage applied to theelectromagnetic valve disappears, the current supplied to the coil 101or 108 of the electromagnetic valve is also stepped down to the zerolevel, and in this case too, a time lag of first order T₂ appears alsoin the stroke of the plunger or needle valve member of theelectromagnetic valve due to, for example, the repulsive force of thecoil spring 105 or 113. These time lags T₁ and T₂ will take variousvalues depending on the factors including the number of turns and wirediameter of the coils and the spring constant of the coil springs in theelectromagnetic valves. In most of commonly employed electromagneticvalves of the types above described, the time lag T₁ is approximatelyequal to the time lag T₂ or T₁ ≈T₂. In the present specification, asymbol T₀ is used to generally represent T₁ and T₂.

FIG. 5 is a circuit diagram of an embodiment of the control device ofthe present invention which is preferably used for the control of aproportional electromagnetic valve having such a first-order time lagcharacteristic. FIGS. 4C, 4D and FIGS. 6A, 6B, 6C show operatingwaveforms at various parts of the electromagnetic valve when the dutycycle of a pulse voltage applied to the electromagnetic valve is varied.

The structure and operation of the circuit shown in FIG. 5 will bedescribed at first. Referring to FIG. 5, a pulse signal generator 207capable of generating a pulse voltage having a variable pulse width(which generator is commonly known per se) is connected with an inputterminal 204. A transistor 203 is turned on in response to theapplication of the voltage to the input terminal 204, and a DC voltageof, for example, 12 volts is applied from a DC power source through aresistor 201 to the coil 202 of the electromagnetic valve. A diode 205is connected in parallel with the coil 202. FIG. 4C shows, by way ofexample, the waveform of the pulse voltage V applied to the inputterminal 204, and FIG. 4D shows the stroke characteristic of, forexample, the plunger or needle valve member of the electromagnetic valvewhen the valve responds to the pulse voltage V having the waveform shownin FIG. 4C. In an ordinary proportional electromagnetic valve, T₀ isabout 15 to 20 msec. Suppose now that the pulse interval or period ofthe pulse voltage V applied to the electromagnetic valve is set at T₃(FIG. 4C) shorter than T₀, then, the duty cycle is given by T₄ /T₃ aswill be readily seen in FIG. 4C. In this case, the stroke characteristicof the plunger or needle valve member of the electromagnetic valve is asshown in FIG. 4D. The value of the applied voltage V shown in FIG. 4Cdiffers from that shown in FIG. 4A in order to attain the equalitybetween the full stroke value S_(F) shown in FIG. 4D and that shown inFIG. 4B. When the duty cycle is varied to, for example, T₅ /T₃ and T₆/T₃ as shown by the one-dot chain line and dotted line respectively inFIG. 6A, the current I supplied to the coil of the electromagnetic valvemakes corresponding variations as shown in FIG. 6B, and the stroke S ofthe plunger or needle valve member of the electromagnetic valve makesalso corresponding variations as shown in FIG. 6C. It will be seen fromFIGS. 6A, 6B and 6C that the amplitude of vibration in the stroke of theplunger or needle valve member of the electromagnetic valve is W₁, W₂and W₃ when the duty cycle is T₆ /T₃ (shown by the dotted line), T₄ /T₃(shown by the solid line) and T₅ /T.sub. 3 (shown by the one-dot chainline) respectively. It will thus be seen that the amplitude of vibrationin the stroke is smaller when the duty cycle is T₆ /T₃ and T₅ /T₃ thanwhen the duty cycle is T₄ /T₃. This fact is also illustrated in FIG. 7Cdescribed later.

Thus, the effective value of current supplied to the coil of theelectromagnetic valve can be varied by varying the duty cycle, and thestroke of the plunger or needle valve member of the electromagneticvalve can also be varied, and yet its vibration can be maintained alwaysat a very small amplitude (W₁, W₂, W₃). This very small amplitude ofvibration (W₁, W₂, W₃) decreases gradually as the value of the period T₃is decreased relative to that of the time lag T₀, and the very smallamplitude of vibration approaches a value very close to zero when thefrequency is, for example, about 200 Hz, that is, when the period T₃ isabout 5 msec. The very small amplitude of vibration (W₁, W₂, W₃) shownin FIG. 6C is depicted as having a considerably large value since theperiod T₃ is supposed to be considerably long relative to the time lagT₀. It is to be added that the drawing is prepared under theconsideration that exaggerated illustration of the very small amplitudeof vibration on the drawing will facilitate the understanding of thebasic principle of the present invention.

Means for providing a variable pulse width of the pulse signal generatedby the pulse signal generator 207, that is, means for providing avariable duty cycle is already commonly known in the art, and therefore,such means is not especially illustrated.

FIG. 7A shows the relation between the duty cycle and the effectivevalue I_(F) of current supplied to the coil of the proportionalelectromagnetic valve shown in FIG. 2 or 3 when the input voltageapplied to the electromagnetic valve has a constant period of, forexample, T₃ shorter than the minimum response time T₀ required for thedisplacement of the plunger or needle valve member over its full stroke,and the duty cycle of the input voltage is varied, provided that T₀ isabsolutely greater than T₃. It will be seen from FIG. 7A that theeffective current value I_(F) is substantially exactly proportional tothe duty cycle. The effective value I_(F) of current supplied to thecoil of the electromagnetic valve and the stroke S of the plunger orneedle valve member of the electromagnetic valve have also aproportional relation as shown in FIG. 7B. FIG. 7C is a graph showingthe relation between the duty cycle D of the input voltage and thestroke S of the plunger or needle valve member of the electromagneticvalve, and it will be seen that there is also a proportional relationtherebetween like FIGS. 7A and 7B. However, as described with referenceto FIGS. 4C, 4D and FIGS. 6A, 6B, 6C, the very small amplitude ofvibration (W₁, W₂, W₃) is depicted in regard to the case of T₀ =T₃instead of T₀ >>T₃ in order to exaggerate the vibration amplitude fromthe standpoint of preparation of a drawing which facilitates theunderstanding of the basic principle of the present invention.

FIG. 8 is a circuit diagram of another embodiment of the control deviceaccording to the present invention. Referring to FIG. 8, two pulsesignals having exactly opposite duty cycles are generated by a knownpulse signal generator 309 to be applied to a pair of signal inputterminals 301 and 302 respectively. The on-state of the first pulsesignal applied to the input terminal 301 is, for example, 70% of onecycle, while that of the second pulse signal applied to the inputterminal 302 is, for example, 30% of one cycle as seen in FIG. 8. Thus,there is a ratio of 7:3 between the on-state period of the voltageapplied to the base of a transistor 303 and the on-state period of thevoltage applied to the base of another transistor 304, and apparently,70% of current is supplied from a power supply terminal 305 of 12 voltsto a proportional electromagnetic valve 308 through a resistor 307 andflows to the transistor 303. On the other hand, the remaining 30% ofcurrent is supplied to the proportional electromagnetic valve 308through another resistor 306 and flows to the transistor 304. When,conversely, the on-state period of the input voltage applied to the baseof the transistor 304 is longer than that of the input voltage appliedto the base of the transistor 303, the proportion of current supplied tothe coil of the electromagnetic valve is apparently greater in theformer case than in the latter. Therefore, when the ratio beween theperiod of current flow to the transistor 303 and that to the transistor304 is 7:3, the plunger or needle valve member of the electromagneticvalve is displaced to make its full stroke in the positive and negativedirections at the rates of 70% and 30% respectively of the total period.However, due to the fact that the input voltage is actually turnedon-off at a period sufficiently shorter than the minimum response timerequired for the full stroke (the maximum stroke in the positive ornegative direction from the neutral position) of the plunger or needlevalve member of the electromagnetic valve, the plunger or needle valvemember of the electromagnetic valve makes an average stroke in thepositive direction which meets the ratio above described. FIG. 9 showsthe stroke characteristic of the electromagnetic valve when the ratiobetween the duty cycles of the two input signals is varied in the mannerdescribed. The positive direction portion of the horizontal axis in FIG.9 represents the duty cycle of the voltage applied to the input terminal301, while the negative direction portion of the horizontal axisrepresents the duty cycle of the voltage applied to the input terminal302. The duty cycle D₃₀₂ of the voltage applied to the input terminal302 is D₃₀₂ =1 when the duty cycle D₃₀₁ of the voltage applied to theinput terminal 301 is D₃₀₁ =0, and in this case, the current flowsentirely to the transistor 304 to maintain the plunger or needle valvemember of the electromagnetic valve at the position displaced over itsfull stroke in the negative direction. On the other hand, D₃₀₂ =0 whenD₃₀₁ =1, and in such a case, the current flows entirely to thetransistor 303 to maintain the plunger or needle valve member at theposition displaced over its full stroke in the position direction. WhenD₃₀₁ =0.5 and D₃₀₂ =0.5, the plunger or needle valve member of theelectromagnetic valve is maintained at the neutral position 0 betweenthe positive stroke +S and the negative stroke -S.

It will be understood from the above-description that the control deviceshown in FIG. 8 comprises a pair of switching elements of respectivelyopposite on-off states for the on-off of inputs applied thereto, so thatthe flowing direction of current supplied to the coil of theelectromagnetic valve can be varied depending on the ratio between theduty cycles of the inputs applied to these two switching elements, andthe plunger or needle valve member of the electromagnetic valve can makeboth the positive stroke and the negative stroke. It is apparent thatthe stroke characteristic shown in FIG. 9 is similar to that shown inFIG. 7C in that it includes a very small vibratory stroke component Wwhich is effective in obviating the hysteresis of the stroke encounteredhitherto. The current supplied to the coil of the electromagnetic valvemust be stabilized in order to ensure the accuracy of the proportionalrelation shown in FIGS. 7C and 9. Provision of a battery will generallysatisfy this requirement, but it is desirable to provide aconstant-voltage source or a constant-current source in order to furtherimprove the accuracy of the proportional relation.

One of the features of the embodiment shown in FIGS. 8 and 9 is that thesafety can be ensured when the element, for example, the needle valvemember is arranged to be restored to a suitable least dangerousposition, (for example, the neutral position 0 in FIG. 9) in the eventof a dangerous situation in which the coil of the electromagnetic valveis not properly energized due to failure of the control circuit.

FIGS. 10 to 15 illustrate preferred applications of the control deviceof the present invention to the control of proportional electromagneticvalves in various control systems. Therefore, the drawings and relatedexplanations will be briefly described.

FIG. 10 shows diagrammatically a control system which employsproportional electromechanical transducers as actuating means for theclosed-loop air-fuel ratio control in a carburetor utilizing a ternarycatalyst. The oxygen concentration in the exhaust gas of an internalcombustion engine 17 is detected by an oxygen probe or detector 10, andthe output signal of the detector 10 is applied to the control device ofthe present invention shown by the reference numeral 11. The controldevice 11 controls proportional electromagnetic valves 12 and 13 whichcontrol the open areas of a slow air bleed 15 and a main air bleed 16 ina carburetor 14 respectively, so that the air-fuel ratio of the air-fuelmixture supplied from the carburetor 14 to the engine 17 can becontrolled to be substantially equal to the ideal air-fuel ratio. Forthe control of the air-fuel ratio, the open areas of various kinds offuel metering jets including a main fuel jet and a slow fuel jet may becontrolled in lieu of the air bleeds above described so as to equallyeffectively attain the purpose. In a prior art control system employingsuch proportional electromagnetic valves as actuating means, theair-fuel ratio has been controlled by a control circuit which makesdigital processing of an output signal of an oxygen probe or detectorand converts the digital signal into an analog signal which is appliedto the proportional electromagnetic valves after being amplified so asto control the stroke positions of the needle valve members of theproportional electromagnetic valves thereby varying the open areas ofthe fuel metering jets. In contrast to the prior art manner of control,the electromechanical transducer control device according to the presentinvention, which includes the control circuit for controlling the dutycycle of a high-frequency input voltage, is advantageous in that it cancontrol such proportional electromagnetic valves by a digital signaloutput of the control circuit.

Therefore, the present invention eliminates the D-A converter and theconverter output amplifier included in the prior art control circuit.Various advantages are thus provided which include the reduction in thecost and the improvement in the reliability, owing to the reduction ofthe number of electronic parts including the power transistor. In aprior art control system employing a proportional electromagnetic valve,the stroke position of the needle valve member of the proportionalelectromagnetic valve has been varied by controlling the quantity ofanalog current. Thus, according to such a control method, theproportional electromagnetic valve has tended to operate with theso-called hysteresis characteristic such that the needle valve member isnot displaced to the stroke position corresponding to the quantity ofanalog current due to the state friction against the movement of theneedle valve member of the electromagnetic valve. In the closed-loopair-fuel ratio control system, the air-fuel ratio must be controlled tobe very close to the ideal air-fuel ratio of about A/F=14.7±0.2 in orderthat the ternary catalyst can exhibit the exhaust gas purificationefficiency of more than about 90% for each of CO, HC and NOx. Thecontrol allowance for the air-fuel ratio A/F is limited to a very smallvalue of about ±0.2, because a variation of the air-fuel ratio beyondthis limit results in a sharp reduction in the purification efficiencyof the ternary catalyst. Therefore, the presence of hysteresis in thestroke characteristic of the electromagnetic valve results inimpossibility of controlling the air-fuel ratio to within the very smallcontrol allowance range above specified, and it becomes inevitable tooperate the engine in the air-fuel ratio region in which the exhaust gaspurification efficiency of the ternary catalyst is considerably reduced.This leads to impossibility of removal of toxic components of theexhaust gas with the desired high efficiency.

In sharp contrast to the prior art control system, the desired controlcan be achieved in the control system employing the electromechanicaltransducer control device according to the present invention. Asdescribed in detail with reference to FIGS. 6A, 6B and 6C, and as alsoadditionally described with reference to FIG. 7C and FIG. 9, theproportional electromagnetic valve operates with a stroke characteristicincludes a very small vibratory stroke component W as shown in FIG. 7Cand FIG. 9, and this very small vibratory stroke component W acts toabsorb the static friction against the movement of the plunger or needlevalve member of the electromagnetic valve so that the source of thehysteresis can be substantially completely eliminated to substantiallycompletely obviate the hysteresis in the stroke characteristic.Therefore, the proper mechanical quantity, that is, the strokecharacteristic corresponding exactly to the instruction provided by theinstruction signal applied from the control circuit can be obtained, andthe delicate control for limiting the air-fuel ratio A/F to within thecontrol allowance range of about ±0.2 can be attained to permitpurification of the exhaust gas with the desired high efficiency of morethan about 90% for each of CO, HC and NOx.

FIG. 11 shows part of a control system similar to that shown in FIG. 10,but in which a single proportional electromagnetic valve is used forcontrolling the open areas of a plurality of metering jets provided in acarburetor for the control of the air-fuel ratio. Referring to FIG. 11,a proportional electromagnetic valve 20 actuates a pair of needle valvemembers 21 and 22 simultaneously for simultaneously controlling the openareas of associated metering jets 23 and 24 at their predeterminedvalues. The electromechanical transducer control device according to thepresent invention is also equally effectively applicable to such acontrol system. Especially when an arrangement as shown in FIG. 11 isemployed, the needle value members tend to encounter a great frictionalresistance by engagement with the openings of the associated meteringjets, and the degree of hysteresis in the stroke characteristic tends tobecome greater than when a needle valve member is associated with ametering jet as shown in FIG. 10. The notable effect of the presentinvention is more markedly exhibited when applied to such a controlsystem.

FIG. 12 shows diagrammatically an engine combustion control systemprovided with a microcomputer, in which the electromechanical transducercontrol device according to the present invention is employed as anactuating means for the control of the recycled quantity of the exhaustgas of an internal combustion engine. The recycled quantity of theexhaust gas must be controlled to be optimum within a range in which theengine parameters such as the output and drivability and the desiredpurification or removal of NOx in the exhaust gas are both satisfied forall the operating conditions of the engine. In the control system shownin FIG. 12, a detector 30 detects the angular position of rotation of anair quantity regulating valve 25 to detect the quantity of intake airsupplied to the engine, and the output signal of this detector 30 isapplied to a control device 42 to be converted into a digital signalrequired for operating a proportional electromagnetic valve 31 in amanner as described with reference to the control device of the presentinvention. This digital signal controls the proportional electromagneticvalve 31, and a flat valve member 32 connected with the plunger of thiselectromagnetic valve 31 is actuated in turn so as to control the gapbetween a flat valve seat 33 and the flat valve member 32. As aconsequence of the control of the gap between the valve seat 33 and theflat valve member 32, the suction negative pressure derived from thedownstream side of a throttle valve 34 and supplied into a diaphragmchamber 37 of an EGR (exhaust gas recycle) valve 36 (commonly called aconstant flow-rate valve) through an orifice 35 is varied inproportional relation to the quantity of intake air, and this controllednegative pressure is used as a power source for displacing a diaphragm38. A needle valve member 39 connected with the diaphragm 38 isdisplaced to vary the open area or gap between this needle valve member39 and an associated valve seat 40 thereby controlling the quantity ofexhaust gas recycled into an intake duct 41. In order that the engineoutput (drivability) and the desired purification of NOx in the exhaustgas can be both satisfied, it is necessary to control the recycledexhaust quantity with an accuracy of about ±5% in all the operatingconditions of the engine (the operating region of the ECR valve).Therefore, the prior art method of controlling the proportionalelectromagnetic valve, according to which the stroke position of thevalve member is controlled depending on the analog current quantity, hasbeen defective in that the hysteresis appearing in the strokecharacteristic due to the frictional resistance encountered by theplunger or needle valve member of the electromagnetic valve makesdifficult to obtain the control accuracy above specified, and therecycled quantity of the exhaust gas tends to be controlled at a valuewhich affects adversely either the engine output requirement or the NOxpurification requirement. In sharp contrast to the prior art manner ofcontrol, the employment of the electromechanical transducer controldevice according to the present invention in such a control system iseffective in substantially completely obviating the hysteresis in thestroke characteristic of the electromagnetic valve as described indetail with reference to FIGS. 6A, 6B, 6C, FIG. 7C and FIG. 9.Therefore, the mechanical quantity is properly proportional to theinstruction provided by the instruction signal applied from the controlcircuit to maintain the accuracy of control to within the very smallrange above specified, so that the engine output requirement and the NOxpurification requirement can both be satisfied.

It is apparent that the effect of application of the electromechanicaltransducer control device of the present invention as an actuating meansfor the air-fuel ratio control in an engine combustion control systemprovided with a microcomputer is similar to that exhibited by itsapplication to the control system described in detail with reference toFIG. 10.

The electromechanical transducer control device according to the presentinvention is also similarly effectively applicable to various controlsystems as described below.

FIG. 13 shows part of a control system in which the analog mechanicalquantity or the stroke of the plunger or needle valve member of aproportional electromagnetic valve is suitably varied to control apressure, for example, a suction negative pressure of an internalcombustion engine, and this pressure is used as a source of actuating amember such as a diaphragm or a piston which converts a pressure intoreciprocating movement of an element connected therewith so as tocontrol the flow rate of fluid as desired. In such a case, therefore,any substantial force is not required for causing the displacement ofthe diaphragm or piston. However, according to the prior art manner ofcontrol in which the analog current quantity is varied to vary thestroke of the plunger or needle valve member of the electromagneticvalve, the resulting hysteresis exerts a great adverse effect on thestroke of the diaphragm or piston. Such a problem is completely obviatedwhen the method of controlling the proportional electromagnetic valve,that is, the electromechanical transducer control device according tothe present invention is applied to this kind of control, since nohysteresis occurs substantially in the stroke characteristic of theelectromagnetic valve.

Referring to FIG. 13, a needle valve member 44 of a proportionalelectromagnetic valve 43 energized by an input voltage having acontrolled duty cycle as described hereinbefore is used to control thearea of a passage 45 of a pressure P so that a controlled pressure P'can be supplied into a diaphragm chamber 46 containing a diaphragm 48.In response to the application of this controlled pressure P', thediaphragm 48 is displaced to a position at which the force of a returnspring 49 counterbalances the pressure P'. A needle valve member 50fixed to the diaphragm 48 makes corresponding movement to vary the openarea of an orifice 51 which controls the flow rate of air. The referencenumeral 47 designates a throttle. This control method is howeverdefective in that a variation of the pressure P results in acorresponding variation of the pressure P', and the value of current Isupplied to the proportional electromagnetic valve 43 cannot solelydetermine the value of pressure P'. Such a defect is obviated by acontrol method shown in FIG. 14.

Referring to FIG. 14, a negative pressure P is applied to a diaphragm 54to bias the diaphragm 54 to a position at which the force of a returnspring 55 counterbalances the pressure P. A needle valve member 53 of aproportional electromagnetic valve 52 is fixed to the diaphragm 54 tocontrol the open area of the passage of the pressure P so that acontrolled vacuum P' can be supplied to a diaphragm chamber 56containing a diaphragm 59. This negative pressure P' is controlled to beconstant in a manner as described below. Suppose that the value of thenegative pressure P varies in the state in which the negative pressureP' is maintained at a predetermined value. Suppose, for example, thatthe negative pressure P increases from the previous value. Then, thearea of the vacuum passage is narrowed by the needle valve member 53 bythe amount corresponding to the increase in the pressure differentialacross the metering part, so that the quantity of air passing throughthe metering part can be controlled to be constant. Therefore, thenegative pressure acting upon the diaphragm 59 in the vacuum chamber 56can be maintained constant. The reference numerals 57 and 58 designate athrottle and a return spring respectively. Thus, the proportionalelectromagnetic valve 52 operates as a means for maintaining constantthe negative pressure P', so that the force generated in theelectromagnetic valve 52 for actuating the needle valve member 53 cansolely be utilized for controlling the negative pressure P' withoutregard to a variation of the value of negative pressure P. Thus, theflow rate of air can be controlled by displacing a needle valve member60 connected with the diaphragm 59 in proportional relation to thevariation of the negative pressure P' thereby varying the open area ofan orifice 61 by the needle valve member 60. A highly accurate flow ratecontrol can be achieved by the application of the electromechanicaltransducer control device according to the present invention to such acontrol system too, since the present invention can substantiallycomplete obviate the undesirable hysteresis in the mechanical quantityof the kind described.

FIG. 15 shows another application of the electromechanical transducercontrol device according to the present invention as actuating means forthe control of the flow rate of fuel in a mechanical fuel injectionsystem. Referring to FIG. 15, fuel is pumped out of a fuel tank 62 by apump 63 to be supplied under pressure to a metering valve 64, and aproportional electromagnetic valve 65 actuates the metering valve 64 sothat the fuel can be supplied at a flow rate providing a suitableair-fuel ratio between it and the flow rate of air detected by an engineintake air flow detecting means. A pressure regulating valve 67 acts tomaintain constant the pressure acting upon an injection valve 68. Thereference numeral 66 designates a return pipe for the fuel. In the priorart control system, tha air flow-rate signal output of the engine intakeair flow detector is transmitted to the metering valve 64 through amechanical linkage. Thus, the prior art control system has beendefective in that it is subject to structural limitations, and the typeof the air flow detector is also limited. Employment of theelectromechanical transducer control device according to the presentinvention as an actuating means in such a system obviates all theseproblems. The prior art control system has also been defective in thatthe factors including the manufacturing tolerance of the dimensions ofthe link connections render it difficult to attain the reproducibilityof the fuel control characteristic for the individual products since theair flow-rate signal is transmitted to the metering valve by means ofthe mechanical linkage. Application of the electromechanical transducercontrol device according to the present invention to such a prior artmechanical flow-rate control system for the purpose of eliminatingfluctuation of the flow rate of fuel is effective in that the positionof the metering valve can be accurately corrected to improve thereproducibility of the fuel control characteristic.

The present invention provides the following advantages:

(1) In the present invention, an electromechanical transducer such as aproportional electromagnetic valve which provides a mechanical outputcorresponding to an electrical input is energized by a digitalelectrical signal. Therefore, a D-A converter and a converter outputamplifier required for a prior control system using a transducer of thiskind are now unnecessary. Thus, the cost can be reduced, and the numberof electronic parts including especially, the power transistor, can alsobe reduced to improve the reliability of the control circuit.

(2) On-off of the electrical input is repeated at a constant periodshorter than the minimum response time required for the full stroke ofthe plunger or needle valve member displaced by the mechanical output ofthe electromechanical transducer, and the duty cycle of the electricalinput is controlled so as to provide an analog mechanical output orquantity. This analog mechanical quantity includes a very small digitalmechanical quantity component or a very small vibratory stroke componentW which is effective in eliminating the hysteresis occuring in themechanical output of the transducer.

(3) Two switching elements are provided for the cyclic on-off of theelectrical quantity applied to the electromechanical transducer, andelectrical signals having opposite duty cycles are applied to these twoswitching elements respectively. Therefore, the transducer provides ananalog mechanical output or quantity of both the positive direction andthe negative direction depending on the ratio between the duty cycles ofthe electrical inputs applied to the respective switching elements.

(4) Application of the electromechanical transducer control device as anactuating means for the closed-loop air-fuel ratio control in acarburetor utilizing a ternary catalyst can improve the accuracy ofcontrol of the air-fuel ratio, reduce the cost of the control circuitand improve the reliability of the control circuit.

(5) Application of the electromechanical transducer control device as anactuating means for the control of the recycled exhaust gas quantity andalso for the control of the air-fuel ratio in an engine combustioncontrol system provided with a microcomputer can improve the accuracy ofcontrol of the recycled exhaust gas quantity and air-fuel ratio, reducethe cost of the control circuit, and improve the reliability of thecontrol circuit.

(6) One of the drawbacks of an on-off electromagnetic valve is the deadzone (FIG. 1) appearing due to application of an electrical input havinga small duty cycle. Such dead zone can be obviated.

(7) Another drawback of the on-off electromagnetic valve is the crashingsound observed during the return movement of the sliding parts makingreciprocating movement between the minimum and maximum points of thefull stroke. Such sound can be substantially obviated by employing aproportional electromagnetic valve and controlling the duty cycle of anelectrical input thereto. The material wear observed in the proportionalelectromagnetic value is also less than that in the on-offelectromagnetic valve.

(8) The mechanical output of the electromechanical transducer includes avery small digital mechanical quantity or a very small vibratory strokecomponent W of high frequency as described hereinbefore. Thus, thetransducer is not substantially adversely affected by disturbance suchas externally imparted vibration since a great electromagnetic force isgenerated instantaneously.

We claim:
 1. A device for controlling an electromechanical transducercomprising:an electromagnetic valve including an electromagnetic coiland a movable member displaced in proportional relation to an electricalinput signal applied to said electromagnetic coil thereby driving acontrolled element; at least one switching means for chopping theelectrical input signal applied to said electromagnetic coil; and meansfor generating an electrical pulse signal for triggering said switchingmeans, wherein the electrical pulse signal generated by said pulsegenerating means and applied to said switching means has a constantperiod shorter than the minimum response time required for said movablemember to make its predetermined full stroke, and the duty cycle of theelectrical pulse signal applied to said switching means is varied tocause displacement of said movable member in proportional relation tothe variation of the duty cycle, and wherein said switching meanscomprises two switching elements which are arranged so that said movablemember is urged in a first direction when one of said switching elementsis turned on, while said movable member is urged in a second directionopposite to said first direction when the other of said switchingelements is turned on, and one of said switching elements is maintainedin its off-state when the other is placed in its on-state.
 2. A controldevice as claimed in claim 1, wherein the stroke of said movable membervaries in proportional relation to the variation of said duty cycle, anda very small vibratory stroke component is superposed on the stroke ofsaid movable member.
 3. A control device as claimed in claim 1, whereineach of said two switching elements is a transistor having two majorelectrodes and one control electrode, said two transistors beingconnected at their first major electrodes across the two terminals ofsaid electromagnetic coil and also with a power source, at their secondmajor electrodes with ground, and at their control electrodes with thetwo outputs of said pulse generating means respectively, said two pulsesignals having their on-off periods inverted relative to each otherappearing from said two outputs of said pulse generating means.
 4. Acontrol device for controlling fluid flow in an internal combustionengine, comprising:a valve for controlling fluid flow; means fordetecting the operating condition of said internal combustion engine; anelectromagnetic device including an electromagnetic coil and a movablemember to be displaced in proportional relation to electric currentapplied to said electromagnetic coil thereby driving said valve; anelectric source for energizing said electromagnetic coil; at least oneswitching means for chopping current supplied from said source to saidelectromagnetic coil; means for generating an electrical pulse signalcomposed of a plurality of pulses for actuating said switching means,said pulse signal generating means comprising a digital computer forreceiving the output signal from said detecting means as an inputsignal, and for processing quantized digital signals and for convertingthe quantized digital signals to pulse signals, each of said pulseshaving a constant period of 5-15 msec, the constant period being shorterthan a minimum period of time required for said movable member to bemoved by its predetermined full stroke and sufficient for said movablemember to be moved; and means for changing the duty cycle of each ofsaid pulses applied to said switching means, wherein said movable memberis displaced in proportional relation to the duty cycle changed by saidduty cycle changing means.
 5. A control device as claimed in claim 4,wherein said valve for controlling fluid flow is disposed forcontrolling an air flow rate flowing into a carburetor of the internalcombustion engine.
 6. A control device as claimed in claim 4, whereinsaid movable member is provided with a plunger having at least oneneedle valve mounted thereon, and a coil spring is provided forenergizing said plunger with a constant force.
 7. A control device asclaimed in claim 6, wherein two needle valves are mounted on saidplunger.
 8. A control device as claimed in claim 7, wherein saidplurality of pulses for actuating said switching means serve forsuperimposing a very small vibratory stroke component on the stroke ofsaid movable member.
 9. A control device as claimed in claim 4 or claim7, wherein said digital computer is a microcomputer.
 10. A controldevice for controlling fluid flow in an internal combustion engine,comprising:a valve for controlling fluid flow; means for detecting theoperating condition of said internal combustion engine; anelectromagnetic device including an electromagnetic coil and a movablemember to be displaced in proportional relation to electric currentapplied to said electromagnetic coil thereby driving said valve; anelectric source for energizing said electromagnetic coil; at least oneswitching means for chopping current supplied from said source to saidelectromagnetic coil; means for generating an electrical pulse signalcomposed of a plurality of pulses for actuating said switching means,said pulse signal generating means comprising a digital computer forreceiving the output signal from said detecting means as an inputsignal, and for processing quantized digital signals and for convertingthe quantized digital signals to pulse signals, each of said pulseshaving a constant period, the constant period being shorter than aminimum period of time required for the movable member to be moved byits predetermined full stroke and the constant period being one of equalto and longer than a period for said movable member to be moved withoutmechanical hysteresis; and means for changing the duty cycle of each ofsaid pulses applied to said switching means, wherein said movable memberis displaced in proportional relation to the duty cycle changed by saidduty cycle changing means.
 11. A control device as claimed in claim 10,wherein the minimum period of time required for said movable member tobe moved by its predetermined full stroke is the time T₀ and the periodof time for said movable member to be moved without mechanicalhysteresis is T₀ /4.
 12. A control device as claimed in claim 11,wherein the minimum time period T₀ is the time lag of theelectromagnetic device which is 15-20 msec, and the time period T₀ /4for said movable member to be moved without mechanical hysteresis isabout 5 msec. .Iadd.
 13. A control device comprising:electromagneticmeans including an electromagnetic coil and a movable member to bedisplaced in proportional relation to electric current applied to saidelectromagnetic coil thereby driving a control means; an electric sourcefor energizing said electromagnetic coil; at least one switching meansfor chopping current supplied from said source to said electromagneticcoil; means for generating an electrical pulse signal composed of aplurality of pulses for actuating said switching means, each of saidpulses having a constant period shorter than a minimum period of timerequired for said movable member to be moved by its predetermined fullstroke and sufficient for said movable member to be moved; and means forchanging the duty cycle of each of said pulses applied to said switchingmeans, wherein said movable member is displaced in proportional relationto the duty cycle changed by said duty cycle changing means..Iaddend..Iadd.14. A control device as claimed in claim 13, wherein saidplurality of pulses for actuating said switching means serve forsuperimposing a very small vibratory stroke component on the stroke ofsaid movable member..Iaddend. .Iadd.15. A control device as claimed inclaim 13, wherein said constant period is a period of 5-15msec..Iaddend. .Iadd.16. A control device as claimed in claim 13,wherein said control device serves for controlling fluid flow in aninternal combustion engine, said control means controlling the fluidflow, means for detecting the operating condition of said internalcombustion engine, and said pulse signal generating means including adigital computer for receiving the output signal from said detectingmeans as an input signal, and for processing quantized digital signalsand for converting the quantized digital signals to pulsesignals..Iaddend. .Iadd.17. A control device as claimed in claim 16,wherein said control means is disposed for controlling a flow rate ofair flowing into a carburetor of the internal combustionengine..Iaddend. .Iadd.18. A control device as claimed in claim 16,wherein said digital computer is a microcomputer..Iaddend. .Iadd.19. Acontrol device as claimed in claim 16, wherein said control meansincludes a movable element movable in accordance with the movement ofsaid movable member of said electromagnetic means for controlling fluidflow in the internal combustion engine..Iaddend. .Iadd.20. A controldevice comprising:electromagnetic means including an electromagneticcoil and a movable member to be displaced in proportional relation toelectric current applied to said electromagnetic coil thereby driving acontrol means; an electric source for energizing said electromagneticcoil; at least one switching means for chopping current supplied fromsaid source to said electromagnetic coil; means for generating anelectrical pulse signal composed of a plurality of pulses for actuatingsaid switching means, each of said pulses having a constant period, theconstant period being shorter than a minimum period of time required forthe movable member to be moved by its predetermined full stroke and theconstant period being one of equal to and longer than a period for saidmovable member to be moved without mechanical hysteresis; and means forchanging the duty cycle of each of said pulses applied to said switchingmeans, wherein said movable member is displaced in proportional relationto the duty cycle changed by said duty cycle changing means..Iaddend..Iadd.21. A control device as claimed in claim 20, wherein the minimumperiod of time required for said movable member to be moved by itspredetermined full stroke is the time T₀ and the period of time for saidmovable member to be moved without mechanical hysteresis is T₀/4..Iaddend. .Iadd.22. A control device as claimed in claim 21, whereinthe minimum time period T₀ is the time lag of electromagnetic devicewhich is 15-20 msec, and the time period T₀ /4 for said movable memberto be moved without mechanical hysteresis is about 5 msec..Iaddend..Iadd.23. A control device as claimed in claim 20, wherein saidplurality of pulses for actuating said switching means serve forsuperimposing a very small vibratory stroke component on the stroke ofsaid movable member..Iaddend. .Iadd.24. A control device as claimed inclaim 20, wherein said constant period is a period of 5-15msec..Iaddend. .Iadd.25. A control device as claimed in claim 20,wherein said control device serves for controlling fluid flow in aninternal combustion engine, said control means controlling the fluidflow, means for detecting the operating condition of said internalcombustion engine, and said pulse signal generating means including adigital computer for receiving the output signal from said detectingmeans as an input signal, and for processing quantized digital signalsand for converting the quantized digital signals to pulsesignals..Iaddend. .Iadd.26. A control device as claimed in claim 25,wherein said control means is disposed for controlling a flow rate ofair flowing into a carburetor of the internal combustionengine..Iaddend. .Iadd.27. A control device as claimed in claim 25,wherein said digital computer is a microcomputer..Iaddend. .Iadd.28. Acontrol device as claimed in claim 25, wherein said control meansincludes a movable element movable in accordance with the movement ofsaid movable member of said electromagnetic means for controlling fluidflow in the internal combustion engine..Iaddend.